After a period of 4 weeks where it was not used I find I have lost 200 revs off the top end. I had the boat lifted and pressure washed but this has not made any difference (she was pretty clean anyway). All the temps and pressures are OK and nothing looks amiss in the engine space.
Normal max revs 3800 (now 3600), 2.8ltr Cummins Mercruiser Diesel with Bravo three drive.
Any ideas ?